[VPlan] Simplify Plan's entry in removeBranchOnConst. (#154510)

After #153643, there may be a
BranchOnCond with constant condition in the entry block.

Simplify those in removeBranchOnConst. This removes a number of
redundant conditional branch from entry blocks.

In some cases, it may also make the original scalar loop unreachable,
because we know it will never execute. In that case, we need to remove
the loop from LoopInfo, because all unreachable blocks may dominate each
other, making LoopInfo invalid. In those cases, we can also completely
remove the loop, for which I'll share a follow-up patch.

Depends on #153643.

PR: #154510

Author: fhahn

llvm/include/llvm/Transforms/Utils/LoopUtils.h

@@ -533,23 +533,6 @@ LLVM_ABI int rewriteLoopExitValues(Loop *L, LoopInfo *LI,
                                    ReplaceExitVal ReplaceExitValue,
                                    SmallVector<WeakTrackingVH, 16> &DeadInsts);
 
-/// Set weights for \p UnrolledLoop and \p RemainderLoop based on weights for
-/// \p OrigLoop and the following distribution of \p OrigLoop iteration among \p
-/// UnrolledLoop and \p RemainderLoop. \p UnrolledLoop receives weights that
-/// reflect TC/UF iterations, and \p RemainderLoop receives weights that reflect
-/// the remaining TC%UF iterations.
-///
-/// Note that \p OrigLoop may be equal to either \p UnrolledLoop or \p
-/// RemainderLoop in which case weights for \p OrigLoop are updated accordingly.
-/// Note also behavior is undefined if \p UnrolledLoop and \p RemainderLoop are
-/// equal. \p UF must be greater than zero.
-/// If \p OrigLoop has no profile info associated nothing happens.
-///
-/// This utility may be useful for such optimizations as unroller and
-/// vectorizer as it's typical transformation for them.
-LLVM_ABI void setProfileInfoAfterUnrolling(Loop *OrigLoop, Loop *UnrolledLoop,
-                                           Loop *RemainderLoop, uint64_t UF);
-
 /// Utility that implements appending of loops onto a worklist given a range.
 /// We want to process loops in postorder, but the worklist is a LIFO data
 /// structure, so we append to it in *reverse* postorder.

llvm/lib/Transforms/Utils/LoopUtils.cpp

@@ -1865,32 +1865,6 @@ int llvm::rewriteLoopExitValues(Loop *L, LoopInfo *LI, TargetLibraryInfo *TLI,
   return NumReplaced;
 }
 
-/// Set weights for \p UnrolledLoop and \p RemainderLoop based on weights for
-/// \p OrigLoop.
-void llvm::setProfileInfoAfterUnrolling(Loop *OrigLoop, Loop *UnrolledLoop,
-                                        Loop *RemainderLoop, uint64_t UF) {
-  assert(UF > 0 && "Zero unrolled factor is not supported");
-  assert(UnrolledLoop != RemainderLoop &&
-         "Unrolled and Remainder loops are expected to distinct");
-
-  // Get number of iterations in the original scalar loop.
-  unsigned OrigLoopInvocationWeight = 0;
-  std::optional<unsigned> OrigAverageTripCount =
-      getLoopEstimatedTripCount(OrigLoop, &OrigLoopInvocationWeight);
-  if (!OrigAverageTripCount)
-    return;
-
-  // Calculate number of iterations in unrolled loop.
-  unsigned UnrolledAverageTripCount = *OrigAverageTripCount / UF;
-  // Calculate number of iterations for remainder loop.
-  unsigned RemainderAverageTripCount = *OrigAverageTripCount % UF;
-
-  setLoopEstimatedTripCount(UnrolledLoop, UnrolledAverageTripCount,
-                            OrigLoopInvocationWeight);
-  setLoopEstimatedTripCount(RemainderLoop, RemainderAverageTripCount,
-                            OrigLoopInvocationWeight);
-}
-
 /// Utility that implements appending of loops onto a worklist.
 /// Loops are added in preorder (analogous for reverse postorder for trees),
 /// and the worklist is processed LIFO.

llvm/lib/Transforms/Vectorize/LoopVectorizationPlanner.h

@@ -570,12 +570,18 @@ class LoopVectorizationPlanner {
 
   /// Update loop metadata and profile info for both the scalar remainder loop
   /// and \p VectorLoop, if it exists. Keeps all loop hints from the original
-  /// loop on the vector loop and replaces vectorizer-specific metadata.
-  void updateLoopMetadataAndProfileInfo(Loop *VectorLoop,
-                                        VPBasicBlock *HeaderVPBB,
-                                        bool VectorizingEpilogue,
-                                        unsigned EstimatedVFxUF,
-                                        bool DisableRuntimeUnroll);
+  /// loop on the vector loop and replaces vectorizer-specific metadata. The
+  /// loop ID of the original loop \p OrigLoopID must be passed, together with
+  /// the average trip count and invocation weight of the original loop (\p
+  /// OrigAverageTripCount and \p OrigLoopInvocationWeight respectively). They
+  /// cannot be retrieved after the plan has been executed, as the original loop
+  /// may have been removed.
+  void updateLoopMetadataAndProfileInfo(
+      Loop *VectorLoop, VPBasicBlock *HeaderVPBB, const VPlan &Plan,
+      bool VectorizingEpilogue, MDNode *OrigLoopID,
+      std::optional<unsigned> OrigAverageTripCount,
+      unsigned OrigLoopInvocationWeight, unsigned EstimatedVFxUF,
+      bool DisableRuntimeUnroll);
 
 protected:
   /// Build VPlans for power-of-2 VF's between \p MinVF and \p MaxVF inclusive,

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -2347,12 +2347,15 @@ Value *EpilogueVectorizerMainLoop::createIterationCountCheck(
 }
 
 /// Replace \p VPBB with a VPIRBasicBlock wrapping \p IRBB. All recipes from \p
-/// VPBB are moved to the end of the newly created VPIRBasicBlock. VPBB must
-/// have a single predecessor, which is rewired to the new VPIRBasicBlock. All
-/// successors of VPBB, if any, are rewired to the new VPIRBasicBlock.
+/// VPBB are moved to the end of the newly created VPIRBasicBlock. All
+/// predecessors and successors of VPBB, if any, are rewired to the new
+/// VPIRBasicBlock. If \p VPBB may be unreachable, \p Plan must be passed.
 static VPIRBasicBlock *replaceVPBBWithIRVPBB(VPBasicBlock *VPBB,
-                                             BasicBlock *IRBB) {
-  VPIRBasicBlock *IRVPBB = VPBB->getPlan()->createVPIRBasicBlock(IRBB);
+                                             BasicBlock *IRBB,
+                                             VPlan *Plan = nullptr) {
+  if (!Plan)
+    Plan = VPBB->getPlan();
+  VPIRBasicBlock *IRVPBB = Plan->createVPIRBasicBlock(IRBB);
   auto IP = IRVPBB->begin();
   for (auto &R : make_early_inc_range(VPBB->phis()))
     R.moveBefore(*IRVPBB, IP);
@@ -7184,6 +7187,19 @@ DenseMap<const SCEV *, Value *> LoopVectorizationPlanner::executePlan(
   VPlanTransforms::optimizeForVFAndUF(BestVPlan, BestVF, BestUF, PSE);
   VPlanTransforms::simplifyRecipes(BestVPlan);
   VPlanTransforms::removeBranchOnConst(BestVPlan);
+  if (BestVPlan.getEntry()->getSingleSuccessor() ==
+      BestVPlan.getScalarPreheader()) {
+    // TODO: The vector loop would be dead, should not even try to vectorize.
+    ORE->emit([&]() {
+      return OptimizationRemarkAnalysis(DEBUG_TYPE, "VectorizationDead",
+                                        OrigLoop->getStartLoc(),
+                                        OrigLoop->getHeader())
+             << "Created vector loop never executes due to insufficient trip "
+                "count.";
+    });
+    return DenseMap<const SCEV *, Value *>();
+  }
+
   VPlanTransforms::narrowInterleaveGroups(
       BestVPlan, BestVF,
       TTI.getRegisterBitWidth(TargetTransformInfo::RGK_FixedWidthVector));
@@ -7226,7 +7242,7 @@ DenseMap<const SCEV *, Value *> LoopVectorizationPlanner::executePlan(
   // middle block. The vector loop is created during VPlan execution.
   State.CFG.PrevBB = ILV.createVectorizedLoopSkeleton();
   replaceVPBBWithIRVPBB(BestVPlan.getScalarPreheader(),
-                        State.CFG.PrevBB->getSingleSuccessor());
+                        State.CFG.PrevBB->getSingleSuccessor(), &BestVPlan);
   VPlanTransforms::removeDeadRecipes(BestVPlan);
 
   assert(verifyVPlanIsValid(BestVPlan, true /*VerifyLate*/) &&
@@ -7257,6 +7273,13 @@ DenseMap<const SCEV *, Value *> LoopVectorizationPlanner::executePlan(
   //
   //===------------------------------------------------===//
 
+  // Retrieve loop information before executing the plan, which may remove the
+  // original loop, if it becomes unreachable.
+  MDNode *LID = OrigLoop->getLoopID();
+  unsigned OrigLoopInvocationWeight = 0;
+  std::optional<unsigned> OrigAverageTripCount =
+      getLoopEstimatedTripCount(OrigLoop, &OrigLoopInvocationWeight);
+
   BestVPlan.execute(&State);
 
   // 2.6. Maintain Loop Hints
@@ -7270,7 +7293,8 @@ DenseMap<const SCEV *, Value *> LoopVectorizationPlanner::executePlan(
   updateLoopMetadataAndProfileInfo(
       HeaderVPBB ? LI->getLoopFor(State.CFG.VPBB2IRBB.lookup(HeaderVPBB))
                  : nullptr,
-      HeaderVPBB, VectorizingEpilogue,
+      HeaderVPBB, BestVPlan, VectorizingEpilogue, LID, OrigAverageTripCount,
+      OrigLoopInvocationWeight,
       estimateElementCount(BestVF * BestUF, CM.getVScaleForTuning()),
       DisableRuntimeUnroll);
 

llvm/lib/Transforms/Vectorize/VPlan.cpp

@@ -969,12 +969,24 @@ void VPlan::execute(VPTransformState *State) {
   setName("Final VPlan");
   LLVM_DEBUG(dump());
 
-  // Disconnect scalar preheader and scalar header, as the dominator tree edge
-  // will be updated as part of VPlan execution. This allows keeping the DTU
-  // logic generic during VPlan execution.
   BasicBlock *ScalarPh = State->CFG.ExitBB;
-  State->CFG.DTU.applyUpdates(
-      {{DominatorTree::Delete, ScalarPh, ScalarPh->getSingleSuccessor()}});
+  VPBasicBlock *ScalarPhVPBB = getScalarPreheader();
+  if (ScalarPhVPBB->hasPredecessors()) {
+    // Disconnect scalar preheader and scalar header, as the dominator tree edge
+    // will be updated as part of VPlan execution. This allows keeping the DTU
+    // logic generic during VPlan execution.
+    State->CFG.DTU.applyUpdates(
+        {{DominatorTree::Delete, ScalarPh, ScalarPh->getSingleSuccessor()}});
+  } else {
+    Loop *OrigLoop =
+        State->LI->getLoopFor(getScalarHeader()->getIRBasicBlock());
+    // If the original loop is unreachable, we need to delete it.
+    auto Blocks = OrigLoop->getBlocksVector();
+    Blocks.push_back(cast<VPIRBasicBlock>(ScalarPhVPBB)->getIRBasicBlock());
+    for (auto *BB : Blocks)
+      State->LI->removeBlock(BB);
+    State->LI->erase(OrigLoop);
+  }
 
   ReversePostOrderTraversal<VPBlockShallowTraversalWrapper<VPBlockBase *>> RPOT(
       Entry);
@@ -1648,14 +1660,18 @@ static void addRuntimeUnrollDisableMetaData(Loop *L) {
 }
 
 void LoopVectorizationPlanner::updateLoopMetadataAndProfileInfo(
-    Loop *VectorLoop, VPBasicBlock *HeaderVPBB, bool VectorizingEpilogue,
-    unsigned EstimatedVFxUF, bool DisableRuntimeUnroll) {
-  MDNode *LID = OrigLoop->getLoopID();
+    Loop *VectorLoop, VPBasicBlock *HeaderVPBB, const VPlan &Plan,
+    bool VectorizingEpilogue, MDNode *OrigLoopID,
+    std::optional<unsigned> OrigAverageTripCount,
+    unsigned OrigLoopInvocationWeight, unsigned EstimatedVFxUF,
+    bool DisableRuntimeUnroll) {
   // Update the metadata of the scalar loop. Skip the update when vectorizing
-  // the epilogue loop, to ensure it is only updated once.
-  if (!VectorizingEpilogue) {
-    std::optional<MDNode *> RemainderLoopID = makeFollowupLoopID(
-        LID, {LLVMLoopVectorizeFollowupAll, LLVMLoopVectorizeFollowupEpilogue});
+  // the epilogue loop to ensure it is updated only once. Also skip the update
+  // when the scalar loop became unreachable.
+  if (Plan.getScalarPreheader()->hasPredecessors() && !VectorizingEpilogue) {
+    std::optional<MDNode *> RemainderLoopID =
+        makeFollowupLoopID(OrigLoopID, {LLVMLoopVectorizeFollowupAll,
+                                        LLVMLoopVectorizeFollowupEpilogue});
     if (RemainderLoopID) {
       OrigLoop->setLoopID(*RemainderLoopID);
     } else {
@@ -1670,15 +1686,15 @@ void LoopVectorizationPlanner::updateLoopMetadataAndProfileInfo(
   if (!VectorLoop)
     return;
 
-  if (std::optional<MDNode *> VectorizedLoopID =
-          makeFollowupLoopID(LID, {LLVMLoopVectorizeFollowupAll,
-                                   LLVMLoopVectorizeFollowupVectorized})) {
+  if (std::optional<MDNode *> VectorizedLoopID = makeFollowupLoopID(
+          OrigLoopID, {LLVMLoopVectorizeFollowupAll,
+                       LLVMLoopVectorizeFollowupVectorized})) {
     VectorLoop->setLoopID(*VectorizedLoopID);
   } else {
     // Keep all loop hints from the original loop on the vector loop (we'll
     // replace the vectorizer-specific hints below).
-    if (LID)
-      VectorLoop->setLoopID(LID);
+    if (OrigLoopID)
+      VectorLoop->setLoopID(OrigLoopID);
 
     if (!VectorizingEpilogue) {
       LoopVectorizeHints Hints(VectorLoop, true, *ORE);
@@ -1723,7 +1739,21 @@ void LoopVectorizationPlanner::updateLoopMetadataAndProfileInfo(
   // For scalable vectorization we can't know at compile time how many
   // iterations of the loop are handled in one vector iteration, so instead
   // use the value of vscale used for tuning.
-  setProfileInfoAfterUnrolling(OrigLoop, VectorLoop, OrigLoop, EstimatedVFxUF);
+  if (!OrigAverageTripCount)
+    return;
+  // Calculate number of iterations in unrolled loop.
+  unsigned AverageVectorTripCount = *OrigAverageTripCount / EstimatedVFxUF;
+  // Calculate number of iterations for remainder loop.
+  unsigned RemainderAverageTripCount = *OrigAverageTripCount % EstimatedVFxUF;
+
+  if (HeaderVPBB) {
+    setLoopEstimatedTripCount(VectorLoop, AverageVectorTripCount,
+                              OrigLoopInvocationWeight);
+  }
+  if (Plan.getScalarPreheader()->hasPredecessors()) {
+    setLoopEstimatedTripCount(OrigLoop, RemainderAverageTripCount,
+                              OrigLoopInvocationWeight);
+  }
 }
 
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)

llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp

@@ -2215,10 +2215,12 @@ void VPlanTransforms::removeBranchOnConst(VPlan &Plan) {
   for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(
            vp_depth_first_shallow(Plan.getEntry()))) {
     VPValue *Cond;
-    if (VPBB->getNumSuccessors() != 2 || VPBB == Plan.getEntry() ||
-        !match(&VPBB->back(), m_BranchOnCond(m_VPValue(Cond))))
+    // Skip blocks that are not terminated by BranchOnCond.
+    if (VPBB->empty() || !match(&VPBB->back(), m_BranchOnCond(m_VPValue(Cond))))
       continue;
 
+    assert(VPBB->getNumSuccessors() == 2 &&
+           "Two successors expected for BranchOnCond");
     unsigned RemovedIdx;
     if (match(Cond, m_True()))
       RemovedIdx = 1;

llvm/test/Transforms/LoopVectorize/AArch64/aarch64-predication.ll

@@ -52,8 +52,8 @@ define i64 @predicated_udiv_scalarized_operand(ptr %a, i64 %x) {
 ; CHECK-NEXT:    [[TMP17]] = add <2 x i64> [[VEC_PHI]], [[PREDPHI]]
 ; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 2
 ; CHECK-NEXT:    [[TMP18:%.*]] = icmp eq i64 [[INDEX_NEXT]], 100
-; CHECK-NEXT:    br i1 [[TMP18]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
-; CHECK:       middle.block:
+; CHECK-NEXT:    br i1 [[TMP18]], label [[FOR_END:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
+; CHECK:       for.end:
 ; CHECK-NEXT:    [[TMP19:%.*]] = call i64 @llvm.vector.reduce.add.v2i64(<2 x i64> [[TMP17]])
 ; CHECK-NEXT:    ret i64 [[TMP19]]
 ;

llvm/test/Transforms/LoopVectorize/AArch64/blend-costs.ll

@@ -180,8 +180,8 @@ exit:
 define void @test_blend_feeding_replicated_store_2(ptr noalias %src, ptr %dst, i1 %c.0) {
 ; CHECK-LABEL: define void @test_blend_feeding_replicated_store_2(
 ; CHECK-SAME: ptr noalias [[SRC:%.*]], ptr [[DST:%.*]], i1 [[C_0:%.*]]) {
-; CHECK-NEXT:  [[ENTRY:.*]]:
-; CHECK-NEXT:    br i1 false, label %[[SCALAR_PH:.*]], label %[[VECTOR_PH:.*]]
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    br label %[[VECTOR_PH:.*]]
 ; CHECK:       [[VECTOR_PH]]:
 ; CHECK-NEXT:    [[BROADCAST_SPLATINSERT:%.*]] = insertelement <16 x i1> poison, i1 [[C_0]], i64 0
 ; CHECK-NEXT:    [[BROADCAST_SPLAT:%.*]] = shufflevector <16 x i1> [[BROADCAST_SPLATINSERT]], <16 x i1> poison, <16 x i32> zeroinitializer
@@ -344,12 +344,11 @@ define void @test_blend_feeding_replicated_store_2(ptr noalias %src, ptr %dst, i
 ; CHECK-NEXT:    [[TMP71:%.*]] = icmp eq i32 [[INDEX_NEXT]], 96
 ; CHECK-NEXT:    br i1 [[TMP71]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP4:![0-9]+]]
 ; CHECK:       [[MIDDLE_BLOCK]]:
-; CHECK-NEXT:    br label %[[SCALAR_PH]]
+; CHECK-NEXT:    br label %[[SCALAR_PH:.*]]
 ; CHECK:       [[SCALAR_PH]]:
-; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i32 [ 96, %[[MIDDLE_BLOCK]] ], [ 0, %[[ENTRY]] ]
 ; CHECK-NEXT:    br label %[[LOOP_HEADER:.*]]
 ; CHECK:       [[LOOP_HEADER]]:
-; CHECK-NEXT:    [[IV1:%.*]] = phi i32 [ [[BC_RESUME_VAL]], %[[SCALAR_PH]] ], [ [[IV_NEXT:%.*]], %[[LOOP_LATCH:.*]] ]
+; CHECK-NEXT:    [[IV1:%.*]] = phi i32 [ 96, %[[SCALAR_PH]] ], [ [[IV_NEXT:%.*]], %[[LOOP_LATCH:.*]] ]
 ; CHECK-NEXT:    [[GEP_SRC1:%.*]] = getelementptr inbounds i8, ptr [[SRC]], i32 [[IV1]]
 ; CHECK-NEXT:    [[L:%.*]] = load i8, ptr [[GEP_SRC1]], align 1
 ; CHECK-NEXT:    [[C_1:%.*]] = icmp eq i8 [[L]], 0

llvm/test/Transforms/LoopVectorize/AArch64/call-costs.ll

@@ -6,8 +6,8 @@ target triple = "arm64-apple-macosx11.0.0"
 define void @fshl_operand_first_order_recurrence(ptr %dst, ptr noalias %src) {
 ; CHECK-LABEL: define void @fshl_operand_first_order_recurrence(
 ; CHECK-SAME: ptr [[DST:%.*]], ptr noalias [[SRC:%.*]]) {
-; CHECK-NEXT:  [[ENTRY:.*]]:
-; CHECK-NEXT:    br i1 false, label %[[SCALAR_PH:.*]], label %[[VECTOR_PH:.*]]
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    br label %[[VECTOR_PH:.*]]
 ; CHECK:       [[VECTOR_PH]]:
 ; CHECK-NEXT:    br label %[[VECTOR_BODY:.*]]
 ; CHECK:       [[VECTOR_BODY]]:
@@ -30,14 +30,12 @@ define void @fshl_operand_first_order_recurrence(ptr %dst, ptr noalias %src) {
 ; CHECK-NEXT:    br i1 [[TMP14]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
 ; CHECK:       [[MIDDLE_BLOCK]]:
 ; CHECK-NEXT:    [[VECTOR_RECUR_EXTRACT:%.*]] = extractelement <2 x i64> [[WIDE_LOAD1]], i32 1
-; CHECK-NEXT:    br label %[[SCALAR_PH]]
+; CHECK-NEXT:    br label %[[SCALAR_PH:.*]]
 ; CHECK:       [[SCALAR_PH]]:
-; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ 100, %[[MIDDLE_BLOCK]] ], [ 0, %[[ENTRY]] ]
-; CHECK-NEXT:    [[SCALAR_RECUR_INIT:%.*]] = phi i64 [ [[VECTOR_RECUR_EXTRACT]], %[[MIDDLE_BLOCK]] ], [ 0, %[[ENTRY]] ]
 ; CHECK-NEXT:    br label %[[LOOP:.*]]
 ; CHECK:       [[LOOP]]:
-; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ [[BC_RESUME_VAL]], %[[SCALAR_PH]] ], [ [[IV_NEXT:%.*]], %[[LOOP]] ]
-; CHECK-NEXT:    [[RECUR:%.*]] = phi i64 [ [[SCALAR_RECUR_INIT]], %[[SCALAR_PH]] ], [ [[L:%.*]], %[[LOOP]] ]
+; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ 100, %[[SCALAR_PH]] ], [ [[IV_NEXT:%.*]], %[[LOOP]] ]
+; CHECK-NEXT:    [[RECUR:%.*]] = phi i64 [ [[VECTOR_RECUR_EXTRACT]], %[[SCALAR_PH]] ], [ [[L:%.*]], %[[LOOP]] ]
 ; CHECK-NEXT:    [[GEP_SRC:%.*]] = getelementptr inbounds i64, ptr [[SRC]], i64 [[IV]]
 ; CHECK-NEXT:    [[L]] = load i64, ptr [[GEP_SRC]], align 8
 ; CHECK-NEXT:    [[OR:%.*]] = tail call i64 @llvm.fshl.i64(i64 1, i64 [[RECUR]], i64 1)
@@ -73,7 +71,7 @@ define void @powi_call(ptr %P) {
 ; CHECK-LABEL: define void @powi_call(
 ; CHECK-SAME: ptr [[P:%.*]]) {
 ; CHECK-NEXT:  [[ENTRY:.*:]]
-; CHECK-NEXT:    br i1 false, label %[[SCALAR_PH:.*]], label %[[VECTOR_PH:.*]]
+; CHECK-NEXT:    br label %[[VECTOR_PH:.*]]
 ; CHECK:       [[VECTOR_PH]]:
 ; CHECK-NEXT:    br label %[[VECTOR_BODY:.*]]
 ; CHECK:       [[VECTOR_BODY]]:
@@ -83,7 +81,7 @@ define void @powi_call(ptr %P) {
 ; CHECK-NEXT:    br label %[[MIDDLE_BLOCK:.*]]
 ; CHECK:       [[MIDDLE_BLOCK]]:
 ; CHECK-NEXT:    br label %[[EXIT:.*]]
-; CHECK:       [[SCALAR_PH]]:
+; CHECK:       [[SCALAR_PH:.*]]:
 ; CHECK-NEXT:    br label %[[LOOP:.*]]
 ; CHECK:       [[LOOP]]:
 ; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ 0, %[[SCALAR_PH]] ], [ [[IV_NEXT:%.*]], %[[LOOP]] ]
@@ -93,7 +91,7 @@ define void @powi_call(ptr %P) {
 ; CHECK-NEXT:    store double [[POWI]], ptr [[GEP]], align 8
 ; CHECK-NEXT:    [[IV_NEXT]] = add i64 [[IV]], 1
 ; CHECK-NEXT:    [[EC:%.*]] = icmp eq i64 [[IV]], 1
-; CHECK-NEXT:    br i1 [[EC]], label %[[EXIT]], label %[[LOOP]], !llvm.loop [[LOOP4:![0-9]+]]
+; CHECK-NEXT:    br i1 [[EC]], label %[[EXIT]], label %[[LOOP]]
 ; CHECK:       [[EXIT]]:
 ; CHECK-NEXT:    ret void
 ;
@@ -224,5 +222,4 @@ declare i64 @llvm.fshl.i64(i64, i64, i64)
 ; CHECK: [[META1]] = !{!"llvm.loop.isvectorized", i32 1}
 ; CHECK: [[META2]] = !{!"llvm.loop.unroll.runtime.disable"}
 ; CHECK: [[LOOP3]] = distinct !{[[LOOP3]], [[META2]], [[META1]]}
-; CHECK: [[LOOP4]] = distinct !{[[LOOP4]], [[META2]], [[META1]]}
 ;.